Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2000-11-17
2002-08-20
Hampton-Hightower, P. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S034200, C428S034600, C428S034700, C428S036910, C428S411100, C428S475500, C428S475800, C264S080000, C264S446000, C264S454000, C264S455000, C264S513000, C264S515000, C264S516000, C156S082000, C156S244230, C156S327000
Reexamination Certificate
active
06436547
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a laminated packaging material comprising a core layer of paper or paperboard and a gas barrier layer of polyamide, including a condensation polymer of metaxylene diamine and adipic acid (Nylon-MXD6), applied on one side of the core layer together with at least one layer of heat sealable plastics by means of co-extrusion coating.
The present invention also relates to a method of manufacturing of the laminated packaging material according to the invention as well as to a packaging container which is produced from the laminated packaging material.
BACKGROUND ART
Within the packaging industry, it is well known to employ laminated packaging material of a single-use nature for the packaging and transport of liquid foods. Normally, such laminated packaging materials are built-up from a configurationally rigid but foldable core layer consisting, for example, of paper or paperboard in order to achieve good mechanical configurational stability. Liquid-tight coatings of plastic are applied on both sides of the core layer and effectively protect the core layer of liquid-absorbing fibres against penetration by moisture. These outer layers normally consist of thermoplastic, preferably polyethylene, which moreover imparts superior thermosealing properties to the packaging material, whereby the packaging material may be converted into finished packages possessing the desired geometric configuration.
Laminated packaging materials consisting solely of paper or paperboard and liquid-Ught plastic lack, however, tightness properties vis-a-vis gases, in particular oxygen gas. This is a major-drawback in the packing of many foods, whose shelf-life, flavour and nutrient content dramatically deteriorate in contact with oxygen gas. One example of such foods is fruit juices whose vitamin C content declines when they are exposed to oxygen gas. In order to provide packaging materials with a barrier against gases, in particular oxygen gas, it is known in the art to apply a layer possessing superior oxygen gas tightness properties, for example aluminium foil (‘Alifoil’), EVOH (ethylene vinyl alcohol) or PVOH (polyvinyl alcohol), on that side of the core layer which is intended to be turned to face towards the interior of the finished package.
It is generally desirable to be able to produce packaging containers for so called “extended shelf life” (ESL) at cooled storage, i.e. to achieve maintained Vitamin C content and quality of the packaged product after about 6 weeks storage at 8° C., about 8 weeks storage at 7° C. or about weeks storage at 4° C.
However, the known gas barriers suffer from certain drawbacks. For example, in certain cases from the points of view of cost, the environment and recycling, it has been deemed appropriate to replace Alifoil as the gas barrier material in food packages. Barrier polymers such as EVOH and PVOH, respectively are highly sensitive to moisture and rapidly lose their barrier properties against oxygen gas when they are exposed to a damp environment. This, among other things, make it necessary to surround gas barrier layers of EVOH and PVOH with layers of another polymer, for instance polyethylene, which is impervious to moisture. Alternatively, EVOH and PVOH, respectively, may be combined with one or more known food approved polymers for forming a continuous, well-integrated layer possessing superior gas barrier properties which are also retained in a damp environment. However, the manufacture of packaging materials including gas barrier layers with EVOH and PVOH, respectively, entails high costs for both material and for the production of the requisite multilayer laminate, since such gas barrier layers must be surrounded by at least one, often two protective outer layers of plastic on each respective side of the laminate.
U.S. Pat. No. 4,777,088 discloses a packaging laminate for the production of juice packages consisting of a core layer of paper or paperboard with a gas barrier layer which is applied thereon and which includes a nylon (not disclosed in any detail), as well as a layer of an ionomer binder, namely Surlyn® applied on the gas barrier layer as an intermediate bonding layer to the innermost (towards the inside of a package) polyolefin layer.
EP 0 520 767 discloses a packaging laminate consisting of a core layer of paper or paperboard and a gas barrier layer including an amorphous polyamide (Selar PA 3426 from DuPont Corp., USA), and a binder layer applied therebetween.
The main drawback with these known packaging laminates is, however, that they do not have sufficiently good gas barrier properties for the purpose of ESL packaging at economical polymer layer thicknesses.
The condensation polyamide polymer of metaxylene diamine and adipic acid, carrying the name “Nylon-MXD6”, is a semi-crystalline polyamide and has special properties as compared with other conventional. polyamides, such as, for example, high tensile and flexural strength and modulus, higher glass transition temperature, lower water absorption, as well as excellent gas barrier properties against, for example, oxygen gas.
U.S. Pat. No. 5,164,267 (abandoned), describes a laminated composite consisting of a substrate sheet based on a cellulosic material laminated with a multilayer film comprising at least one layer based on a polyamide resulting from the polycondensation of aliphatic dicarboxylic acid with xylenediamine, e.g. Nylon-MXD6, wherein the multilayer film is co-extrusion coated onto the substrate with a polyolefin layer being the contact layer to the substrate.
However, it is in fact not possible to employ a gas barrier layer consisting solely of Nylon-MXD6 into liquid food paperboard or carton packaging laminates, since this material provides a brittle layer which readily cracks, for example on forming and folding of the packaging material, and therefore gives a poor barrier towards gases and liquids. Moreover, the Nylon-MXD6 in the gas barrier layer also appears to affect thermosealing properties in the process of sealing of the packaging material into packaging containers negatively, which also results in packages which are less gas-tight.
JP-A-06305086 describes a laminate from a biaxially stretched polyamide film and a paper layer, in which the polyamide film comprises at least two polyamide layers, at least one of the layers containing Nylon-MXD6. The biaxially oriented film is laminated to a paper layer by means of dry lamination methods, employing adhesives, or by means of extrusion lamination. Such a biaxially film is thus pre-manufactured by means of a different process, such as for example film blowing, and then laminated to other layers.
The resulting laminate from JP-A-06305086 is quite different from the one of claim
1
of the present invention. In order to provide adhesion between the paper layer and the polyamide layer, an adhesive, such as urethane adhesive, acrylic adhesive and polyester adhesive, or an intermediate bonding layer must be employed, which in turn requires more and/or different materials in the laminate and thus results in higher production costs and higher environmental impact, from both working environment and nature resource management points of view. Furthermore, the adhesion between the paper layer and the polyamide layer will most likely be worse in such a laminate, since the surface of a pre-manufactured film will be oxidised and/or hardened and will not easily adhere to an extruded bonding layer. In particular, the process is more cumbersome and less cost-effective for producing such a laminate, since it requires an extra step for pre-manufacturing of biaxially oriented film.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to realise a novel, cost-effective, environment friendly and well-integrated, laminated packaging material of the type described by way of introduction, which possesses excellent gas barrier properties, in particular against oxygen gas, as well as good liquid barrier properties and good mechanical properties, such as flexibility and adhesion streng
Postoaca Ion
Toft Nils
Burns Doane Swecker & Mathis L.L.P.
Hampton-Hightower P.
Tetra Laval Holdings & Finance S.A.
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